CASTalk.com

Guest

I'm attempting to interface to an SD card using an AT89S8252 MCU. I'm
using an 74LS125 to convert between 5V and 3.3V. The hardware seems to
be ok since I *do* get a response from the card but I'm having problems
initializing the card in SPI mode.

I am sending 96 clock cycles initially and then I send a CMD0.
Everything I've read suggests that CMD0 should initially respond with
0x01 at which point I can issue CMD1 to take the card out of idle mode.
Sometimes this works. But most of the time it doesn't work.

I usually get 0xFC back from the card and it never returns another
value until I eject the card and re-insert it. At that point CMD0
returns 0x03 and never goes to 0x01. Sometimes I find that if I insert
the card into an SD card reader I have and then reinsert it into my
hardware that the card works as expected (CMD0 returns 0x01, I then
issue CMD1 which returns 0x01 for awhile and then returns 0x00).

The 0x03 response to CMD0 suggests to me it is in idle mode and
reporting an "erase/reset" error. I've been unable to determine what
exactly that means.

At this point I'm running out of ideas of what I could be doing wrong.
I've looked at some code that was written for Atmel AVRs and it appears
I'm doing the same thing. And like I said sometimes it works. But
most of the time it seems the card is in some kind of strange state
that I can't get it out of.

If anyone has any ideas I would be very interested in some suggestions.
Thanks,
Craig

Guest

Never mind. I found the problem. A short between the CS line and
another line was causing the SD card to always be selected. Bad thing.
Problem solved.

Guest

cesgoogle@vaultbbs.com wrote:

Rene Tschaggelar · Guest

howard@zaxcom.com wrote:

	CASTalk.com Forum Index -> Embedded System	All times are GMT
Page 1 of 1